Electrically driven prosthetic elbow



Dec. 22, 1970 R. KATSUREN ELEQTRICALLY DRIVEN PROSTHETIC ELBOW FiledDec. 10, 1968 INVENTOR ROY I. K ATSUREN ATTORNEY United States Patent OUS. Cl. 3-1.1 4 Claims ABSTRACT OF THE DISCLOSURE This invention relatesto an improved electrically driven prosthetic elbow wherein the elbow iscapable of being rigidly locked into place in any desired position, andupon driving the arm to the fully extended position, the elbow isautomatically unlocked.

The invention described herein may be manufactured and used by or forthe Government for governmental purposes without the payment to me ofany royalty thereon.

BACKGROUND OF THE INVENTION The use of external power in human upperextremity prosthesis is rapidly becoming more important for therehabilitation of the severely handicapped. Electrically poweredprosthetic elbows that have been developed to date are generallyself-locking in all functional positions which is not the mostadvantageous design since the amputee in certain situations canexperience discomfort, inconvenience and embarassment due to theinability to unlock the elbow. For example, in the simple act of sittingat a table, a locked prosthetic arm in the fully extended position willcontact the chair before the amputee. In order to avoid this awkwardmovement, the amputee must either swing his arm at the shoulder and letthe arm hang over the side of the chair, or he must drive the elbow to aconvenient flexed position. The choice of letting the arm hang over theside of the chair presents an unnatural position for the amputee and isthus undesirable. With the elbow flexed, however, the amputee must keepin mind that he cannot leave the table by standing directly, but mustfirst be sure that his artificial arm will miss the table. Besides theinconvenience of having to keep these thoughts in mind, the fact thatthe amputee would probably stand with his prosthetic arm in anuncosmetic flexed position presents another undesirable alternative. Thepresent invention is designed to overcome these prior art inconveniencesby allowing the amputee to manipulate his artificial limb in a lifelikemanner with the ability to lock his artificial limb into any desiredposition.

SUMMARY OF THE INVENTION The present invention directs itself to anelectrically powered prosthetic elbow which is designed to overcome thedisadvantages of existing electrically driven prosthetic mechanicalelbows in that the present elbow provides for a simple locking meanswhich will lock in any desired position and which automatically unlockswhen the arm is placed in the fully extended position. This unlockingfeature permits the amputee to simulate normal movement of hisprosthesis and thus overcome the major disadvantage of existing priorart prosthetic elbows,

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cut-away side view of themechanical elbow depicting the locking mechanism in the locked position.

FIG. 2 is an isometric view of the mechanical elbow in the unlockedposition.

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DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now more particularlyto the drawings, in

FIGS. 1 and 2, a reversible direct current motor 1 is connected to speedreducer 3 through connector 2. The motor 1 drives the speed reducer 3which in turn drives worm 5 through a coupling 4. The worm 5 is coveredby the worm cage 6. The motor 1, connector 2, speed reducer 3, coupling4, worm 5 and worm cage 6 are all located in a cavity in the stumpattachment of the prosthetic arm located above the elbow. The worm 5drives gear 7, the combination being self-locking if exterior forcestend to drive the system. Gear hub 8 and its assembly (limiting ring 13,locking lever 10, bracket 17 and bar 11) and shaft 9, which is mountedin the elbow cavity, rotate independently of each other about axis IIexcept when locking lever 10 rests within cavity 26 and bar 11 is in itslocking position (FIG. 1). Plate 27 is affixed to gear hub 8 andprevents bar 11 from moving below its locking position. Unlocking stud12 is capable of rotating bar 11 about fastening pin 24. Locking lever10 is also capable of rotating about fastening pin 28. Spring 16 isaflixed to fastening pin 24. One end of spring 16 is afiixed to pin 18which is rigidly affixed to bracket 17. The other end of spring 16 isaffixed to pin 19 which is rigidly afiixed to bar 11. Limit switchactuators 14 and 22 are designed to actuate switches 15 and 23 whenlimit lobes 20 and 21 respectively of limiting ring 13 come into contactwith the switch actuators.

In the preferred embodiment of the invention, a prosthetic hand andforearm are attached to the elbow such that the vertical motion of thehand and forearm corresponds to the clockwise and counterclockwiserotation of shaft 9 about axis II. A cavity 26 for receiving lockinglever 10 exists within shaft 9 as does a cavity opening 25 exist withingear hub 8. In the unlocked position, FIG. .2, shaft 9 is capable ofvrotation about center axis II independent of gear hub assembly 8, 10,11, 13 and 17. Limiting ring 13, bracket 17 and gear hub 8 are affixedso that they jointly rotate about axis II when driven by power train 1,2, 3, 4, 5, 6 and 7. Support pins 18 and 19 and fastening pin 24 formthe spring holding assembly for spring 16. Locking lever 10 and bar 11are rotatably attached to limiting ring 13 by fastening pins 28 and 24respectively as shown in FIGS. 1 and 2.

In normal operation, the patient starts with the elbow fully extendedwith the artificial arm hanging by his side. FIG. 2 represents thephysical relationships of cavity 26, bar 11, locking lever 10, limitingring 13 and unlocking stud 12 at this fully extended free swingposition. In this position limiting lobe 20 of limiting ring 13 hascontacted limit switch actuator 14 which in turn actuated limit switch15. Limit switch 15 stopped motor 1 thus ending any further rotationabout axis II in a counterclockwise direction of limiting ring 13,locking lever 10, bar 11, gear hub 8- and shaft 9. At this position, bar11 has been forced to rotate in a clockwise manner about fastening pin24 as a direct result of the force applied by unlocking stud 12 to theend of bar 11. The resultant force, applied by unlocking stud 12 to theend of bar 11, is sufficient to overcome the counterclockwise torqueabout fastening pin 24 applied to bar 11 by spring 16. The result is theunlocking of locking lever 10. With bar 11 rotated out of its lockingposition, locking lever 10 is free to rotate about locking pin 28 andout of cavity 26. Gear hub 8, worm gear 7, limiting ring 13, lockinglever 10 and bar 11 depend upon the activation of motor 1 for theirrotation about axis II. However, shaft 9, whose rotation about axis IIis representative of the movement of the artificial forearm and hand, isnot dependent upon motor 1 for movement when bar 11 is 3 forced out ofits locking position as depicted in FIG. 2. In this unlocked position,the patient is able to place his artificial arm into any desiredposition, and upon driving the gear hub 8 and its assembly into alocking position, lock the elbow at that new position.

As the patient begins to place his arm from its fully extended positioninto a desired position, shaft 9 begins to rotate clockwise about axisII. In so doing, the walls of cavity 26 force locking lever 10 to rotatecounterclockwise about fastening pin 28. Since bar 11 has been forced torotate out of its locking position, locking lever 10 is capable ofcounterclockwise movement about fastening pin 28. When the patient hashis artificial arm in the desired position, shaft 9 has been rotatedclockwise about axis II and thus cavity 26 has also been rotated and isno longer in aligment to receive locking lever 10. To lock the elbowinto the new position, the patient actuates motor 1 to cause worm gear7, gear hub 8 with its cavity opening 25, limiting ring 13, lockinglever 10 and bar 11 to rotate clockwise about axis II. As the assemblyrotates clockwise about axis II, bar 11 is no longer brought intocontact with unlocking stud 12. As a result, the overbalancing forceapplied by unlocking stud 12 to bar 11 is removed and the tension ofspring 16 forces bar 11 to rotate counterclockwise about fastening pin24. In this position, bar 11 applies a force to locking lever 10 causinglocking lever 10 to rotate clockwise about fastening pin 28. The bluntend of locking lever 10 is thus forced through gear hub cavity opening25 and is pressed against shaft 9 as locking lever 10 and the rest ofthe gear hub assembly rotate about axis II seeking to bring lockinglever 10 and gear hub cavity opening 25 into alignment with relocatedcavity 26. The patient continues to actuate motor 1 causing the rotationof the gear hub assembly until locking lever 10 locks into place withincavity 26. At this moment, the patient stops the motor and the elbow isnow locked into place. In this position, gear hub cavity opening 25 hasaligned itself with cavity 26, the blunt end of locking lever 10 is nolonger sliding along the circumference of shaft 9 but rather has beenfitted into cavity 26 by the force applied to it by bar 11, and bar 11has rotated counterclockwise about fastening pin 24 and has come to restat its locking position. Plate 27 prevents rotation of bar 11 aboutfastening pin 24 beyond the desired locking position. In this lockedposition, with the motor off, counterclockwise rotation of shaft 9 andthus upward rotation of the artificial arm about the elbow is preventeddue to the inability of shaft 9 to rotate independently of the gear hubassembly when locking lever 10 rests within cavity 26. Clockwiserotation of shaft 9 and thus downward rotation of the artificial armabout the elbow is prevented due to the inability of locking lever 10 tobe rotated out of cavity 26 when bar 11 is in the locked position. Inboth of these cases, power train 1, 2, 3, 4, 5, 6 and 7 provides thelocking effect as it is directly coupled to the elbow mechanism, and inthe deenergized state, the power train provides great frictionalresistance to any external attempts at moving the system. In the lockedposition, the movement of shaft 9 and thus the positioning of theartificial arm is directly controlled by motor 1. The patient can eitherraise or lower his arm depending upon how he operates motor 1. Limits,however, are imposed upon this movement by the interaction of limitingring 13 with its lobes 20 and 21, limit switch actuators 14 and 22 andlimit switches 15 and 23. One limit of movement is being approached inFIG, 1. FIG. 1 represents the approaching of the fully extended armposition. As the limit is reached, lobe of limiting ring 13 comes intocontact with switch actuator 14 which in turn activates switch 15.Switch 15 in turn causes motor 1 to shut off. The other extreme limit ofmovement for the elbow is the position represented by the bending of theelbow to bring the artificial arm and hand up towards the shoulder. Inthis position lobe 21 of limiting ring 13 comes into contact with switchactuator 22 causing switch actuator 22 to actuate switch 23. Switch 23will also cause motor 1 to shut off. Diodes are placed across switches23 and 15 to permit current to flow in a reverse direction thus enablingthe patient to mechanically drive the elbow in an opposite directionafter one of the extreme positions has been reached.

I claim:

1. An electrically driven prosthetic elbow comprising:

(a) an inner rotatable shaft representative of the rotational movementof a prosthetic elbow;

(b) an electrically driven gear hub, said gear hub being independentlyrotatable about said inner shaft;

(0) locking means capable of securing said inner shaft to said gear hub;

((1) switching means capable of controlling the limits of angularmovement of said gear hub; and

(e) means for automatically unlocking said gear hub from said innershaft at one of the limit positions of said gear hub.

2. An electrically driven prosthetic elbow as described in claim 1wherein:

(a) said inner shaft contains a cavity;

(b) said gear hub contains an opening capable of alignment with thecavity of said inner shaft;

(c) a limiting ring is attached to said gear hub;

(a) a first pin is attached to said limiting ring;

(e) a locking lever is rotatably attached to said first pin and alignedso as to be capable of insertion through said gear hub opening into saidinner shaft cavity;

(f) a second pin is attached to said limiting ring;

(g) a bar is rotatably attached to said second pin and in relationshipwith said locking lever so as to have a common surface with said lockinglever; and

(h) a spring is carried by said second pin and in relationship with saidbar so as to cause said bar to place a constant force upon the commonsurface with said locking lever.

3. An electrically driven prosthetic elbow as described in claim 2wherein the switching means comprises:

(a) limit lobes attached to said limiting ring, said limit lobes beingoffset from each other; and

(b) a limit switch in alignment with each of said offset limit lobes,said switches capable when actuated of cutting out an electrical powersource.

4. An electrically driven prosthetic elbow as described in claim 3wherein the unlocking means consists of an unlocking stud aligned withsaid bar so as to force said bar to rotate out of contact with saidlocking lever when said limiting ring approaches one of its limits.

References Cited On the Use of Electricity in Upper ExtremityProstheses, by Colin A. McLaurin, The Journal of Bone and Joint Surgery,vol. 47B, No. 3, August 1965, pp. 448452.

RICHARD A. GAUDET, Primary Examiner R. L. FRINKS, Assistant Examiner s.01. X.R. 3-12.3; 28714, 99; 74 527

